1. Field of Invention
The present invention relates to an antenna. More particularly, the present invention relates to a chip antenna.
2. Description of Related Art
Many modern electronic devices, such as mobile telephones, computers, and network devices, are all provided with functions that communicate signals by wireless communications, following the great progress of the wireless communication science and technology. The main emitting and receiving devices used in wireless communication are signal transceivers and antennas configured thereon. Due to the modern electronic devices becoming lightweight, and small and thin in size, conventional antennas, like rod antennas, Yaki antennas, dish antennas and so on, no longer fill the characteristic requirements of new generation.
Hence, a chip antenna is developed, which has meandered lines and a ceramic material with a designed dielectric constant, to miniaturize the size of the antenna. The chip antenna gradually becomes an indispensable element used in a communication product because of its small size and being directly and easily installed in the electronic devices. But the conventional chip antenna still has some drawbacks, such as a slightly large size, insufficient efficiency, and high manufacturing cost.
The following descriptions uses several related patents to explain what drawbacks or functional imperfections exist in the prior circuit design or manufacturing processes of the conventional chip antenna.
1. Taiwan Patent No. 479852:
The patent discloses a chip antenna, which forms a conductive metal line on a tiny ceramic substrate following the design principle of microline antennas, to minimize the size and volume of the conductive metal line by the high dielectric constant of the ceramic substrate. The conductive metal line is just a flat conductive line with one single input port, not a complete antenna, which needs to associate with an external circuit to work. For example, the chip antenna needs to be installed on a circuit board and associated with an external circuit on the circuit board, thus functioning as an antenna, and the external circuit can be used to adjust the input impedance thereof. However, the chip antenna with a flat metal line does not substantially decrease the size or enhance the efficiency thereof.
2. Taiwan Patent No. 419857:
The patent discloses a surface adhered antenna. This type of antenna also follows the design principle of microline antennas. The lines of the input port and the radiation port are not connected to each other, and the input impedance of the antenna is adjusted by the induction coupling between their conductive lines, thus enhancing the performance of the antenna.
However, the radiation line of the antenna is a simple, flat, meandered line, such as a simple L-shaped or U-shaped meandered line, which cannot effectively decrease the size of the antenna. Moreover, the antenna is a single meandered line with one single input port, the frequency band and bandwidth of which have a poor performance, and the antenna cannot be designed for antenna patterns with different polarizing directions. The applications of the antenna are thus restricted and cannot match varied situations.
3. Taiwan Patent No. 480773:
The patent discloses a chip meandered-lines antenna with multiple substrates. This type of antenna is a three-dimensional antenna structure, and the manufacturing method thereof uses a low temperature cofired ceramic (LTCC) process to manufacture the ceramic substrates.
The ceramic material can be used to minimize the size of the antenna due to its high dielectric constant, but the LTCC process is very complicated. The radiation line of the antenna includes conductive powders positioned on green taps of the ceramic substrates by screen printing, and perforations are created on the ends of the corresponding lines on the adjacent substrates. Conductive materials are used to connect the lines on the upper and lower substrates, thus forming the required three-dimensional antenna structure. Finally, the three-dimensional antenna structure and the ceramic substrates are integrated into a single element by the LTCC process (at about 800° C.–900° C.).
This line design of the type of antenna is based on flat, meandered lines. Several ceramic substrates having flat, meandered lines are prepared. The flat, meandered lines are then connected by perforating holes and electroplating the conductive material to fill them on the ceramic substrates, to form the three-dimensional line. Therefore, the three-dimensional antenna is composed of several flat, meandered lines, and is not easily designed for antenna patterns having a polarizing direction perpendicular to the substrate. In addition, the dielectric constant of the ceramic material usually is limited due to very few materials being suitable for the LTCC process, and the prior art therefore cannot use a ceramic material with a suitable dielectric constant according to different characteristic requirements.
4. Taiwan Patent No. 495106:
The patent discloses a chip antenna, which also is a three-dimensional antenna structure, and is manufactured by the above-described, complicated LTCC process. Several ceramic substrates having flat, meandered lines are prepared. The flat, meandered lines are then connected by perforating holes and electroplating the conductive material to fill them on the ceramic substrates, to form the three-dimensional line. But the line design of the patent is different from that of the former patent. The line design of the former patent is formed by connecting flat, meandered lines on several layers. The line design of this patent is a three-dimensional spiral line, in which conductive lines on every layer are connected to form the three-dimensional spiral structure. But, in whole, the chip antenna of this patent still is a single, meandered line having one single input port.
This type of antenna has the same problems as the antenna of the former patent. Because the LTCC process is applied, the manufacturing method of the antenna is very complicated and the cost thereof is also very high. Moreover, the dielectric constant of the ceramic material usually is limited due to very few materials being suitable to the LTCC process, and the prior art therefore cannot choose the ceramic material with a suitable dielectric constant according to different characteristic requirements. In addition, the three-dimensional antenna is a horizontal and spiral antenna, and therefore it is not easily designed for the antenna patterns having polarizing direction perpendicular to the substrate.